1. Field of the Invention
The invention relates to semi-crystalline films of cycloolefin copolymers, a process for the production of such films and various materials made from such films.
2. Description of Related Art
Cycloolefin copolymers have the following properties that are advantageous specifically for films:
high transparency (for optical uses) PA1 good dielectric properties (as a capacitor dielectric) PA1 good solvent resistance to protic polar solvents, such as water, acetone, alcohols or dimethylformamide, and to aqueous acids and alkalis PA1 high softening temperatures, in particular, at a high cycloolefin content (for high temperature uses) and PA1 good gas barriers (for uses in the packaging sector). PA1 R.sup.9 to R.sup.2 are the same or different and each represent a C.sub.1 -C.sub.16 -alkyl, C.sub.2 -C.sub.6 -alkenyl or C.sub.6 -C.sub.16 -aryl radical, or in wherein the radical pairs R.sup.9 /R.sup.10, R.sup.11 /R.sup.12, R.sup.13 /R.sup.14, R.sup.15 /R.sup.16, R.sup.17 /R.sup.18 and/or R.sup.19 /R.sup.20, together with the carbon atom or atoms to which they are bonded, form a C.sub.4 -C.sub.8 -cycloalkyl radical,
Films prepared from amorphous cycloolefin copolymers are known. Particularly, DD-A 224 538 and DD-A 241 971 describe cast films of ethylene/norbornene copolymers. EP-A 0 384 694 also describes films of cyclic copolymers. Despite a few exceptions, however, the cycloolefinic starting materials mentioned therein all are amorphous.
One primary disadvantage of many amorphous cycloolefin copolymer films is that their solvent resistance is too low with respect to aprotic, nonpolar solvents, such as aliphatic or aromatic hydrocarbons. This disadvantage typically excludes films prepared from these copolymers from many fields of use.
EP-A 384 694 discloses semi-crystalline cycloolefin copolymers having a degree of crystallinity of 0 to 10%, which at the same time are described as having a glass transition temperature of 50.degree. to 230.degree. C. Some experiments have shown, however, that when the catalysts according to EP-A-0 384 694 are used, polyethylene contents, which are semi-crystalline, are formed as a secondary reaction in addition to the amorphous cycloolefin copolymers so that the amorphous cycloolefin copolymer with its added polyethylene content appears overall to be semi-crystalline. The partial crystallinity of the films described therein typically is so low that no melting point can be observed in the DSC measurement curve. It has furthermore been found that the melting point of the cycloolefin copolymers described as semi-crystalline in EP-A 384 694 is below 135.degree. C., which is typical of ethylene sequences. Cycloolefin copolymers which are semi-crystalline as defined in the present invention, however, are not described in EP-A 384 694.
Some of the metallocene catalysts described in EP-A0 503 422 are known to be useful in preparing semi-crystalline cycloolefin copolymer films. During processing via the melt, these products have proven to have low thermal stability that has manifested itself in a brown coloration of the polymer. As thin pressed sheets, these copolymeric films exhibited a significant amount of gel particles (specks), that most likely formed as a result of local crosslinking of the polymer. In addition, clouding has been found which can be attributed to catalyst residues and which reduces the transparency of the product. Attempts to produce films from such polymers, in particular stretching attempts, were unsatisfactory, since the films tore around the specks. Thus, there exists a need to prepare a semi-crystalline cycloolefin copolymeric film that does not suffer from the disadvantages described above.